Although cutting edge critical care technology has been applied in the treatment of Acute Respiratory Distress Syndrome (ARDS), mortality remains at 40%. In theory, ECMO (Extracorporeal Membrane Oxygenation) of blood is continuously an aggressive yet effective treatment for ARDS. The key is obtaining an effective ECMO.
FIG. 1 is a diagram of a heart showing various portions for background purposes. The following brief summary of the heart's circulatory system is included to provide a better understanding of ECMO, and the present invention in particular. The heart 2 receives blood from the upper part of the body through the superior vena cava (SVC) 4 and from the lower part of the body through the larger inferior vena cava (IVC) 6 into the right atrium 12 of the heart. A one-way valve of the IVC 7, known as an Eustachian valve, resists blood flow back into the IVC from the right atrium.
The right atrium 12 then contracts to force the blood through the tricuspid valve 14 into the right ventricle 16. The right ventricle 16 contracts at a relatively small contraction pressure to force the blood through the pulmonary valve 18 into the pulmonary artery 20. The pulmonary artery 20 directs blood to the lungs (not shown) where the blood is oxygenated. From the lungs, the oxygenated blood is returned to the heart 2 through pulmonary vein 22 into the right atrium 24. The right atrium 24, again operating a low pressure, such as less than 18 mm of mercury, pushes the blood through the mitral valve 26 into the left ventricle 28. The left ventricle 28 provides the main pumping chamber for the heart at a higher pressure of approximately 100 mm of mercury. The blood pumped from the left ventricle exits through the aortic valve 30 into the aorta 32 in the lower region known as the aortic root. The aorta 32 then acts as a distribution chamber for the various greater arteries 34.
When the lungs are improperly functioning or not functioning at all, the blood flow through the pulmonary circuit results in poorly oxygenated blood. Oxygenation through ECMO can be necessary. However, proper cannulation is critical for ECMO and the key to its effectiveness and heretofore limitations.
ECMO is divided into two major categories according the cannulation and configuration: Veno-Arterial (VA) ECMO and Veno-venous (VV) ECMO. VA ECMO is more popular because of its effective extracorporeal oxygenation. A drainage cannula is introduced into the superior vena cava and an infusion cannula is introduced into the aorta. Blood is drained through the cannula to a pump, the pump circulates the blood through an oxygenator, and the oxygenated blood is returned to the body through an infusion cannula into the aorta. VA ECMO allows an efficient transfer of oxygen into relatively deoxygenated blood from a vein directly to an artery. However, VA ECMO, which cannulates major arteries, is inherently problematic. Traumatic cannulation of major arteries may lead to ligation and/or occlusion of the major arteries (carotid and femoral arteries), massive arterial bleeding, stroke, or amputation. These inherent risks through cannulation of arteries inhibit the widespread use of VA ECMO. Furthermore, VA ECMO circulates oxygenated blood without passing through the heart. Thus, unsaturated or even deoxygenated blood from the dysfunctional native lungs perfuse the heart myocardium and leads to cardiac stun syndrome.
The primary advantage of VV ECMO over VA ECMO is avoidance of major arterial cannulation and the attendant complications described above. Cannulation of veins for the drainage and infusion avoids the higher pressures and problems of cannulating arteries.
The advantage of avoiding arterial cannulation by VV ECMO has been known, but the technology for implementing a practical VV ECMO has eluded researchers and practitioners. The major disadvantages of VV ECMO include (i) multiple venous cannulation which results in further trauma to the patient, (ii) insufficient venous blood drainage caused by limitations on the drainage cannula placement, and (iii) insufficient extracorporeal gas exchange from undesirable blood recirculation by short circuiting of the blood flow path through the body of oxygenated blood mixed with deoxygenated blood, also due to the limitations on the drainage cannula placement.
There are four types of cannula/cannulation in VV ECMO practice: two site, single lumen cannulation VV ECMO; a single double lumen cannulation (DLVV ECMO); a single cannula tidal flow ECMO; and VVV three cannulation ECMO. All of these types of VV ECMO have the problem of either multi-cannulation and/or blood recirculation.
Two site, single lumen ECMO needs multiple cannulations, one for venous blood drainage and the other for oxygenated blood infusion. The drainage cannula is usually inserted from the jugular vein and lays in the SVC. This procedure is unable to drain more than about half (50%) of the venous blood returning to the heart, because it accesses only the SVC and excludes the IVC. Such a low percentage is generally unable to sustain life. The drainage cannula can be slightly further extended through the SVC into the right atrium to drain more than 50% of the venous blood, because both the SVC and IVC discharge into the atrium. However, that extension increases undesirable recirculation of oxygenated blood as the extracorporeal oxygenated blood is returned into the same location, that is, the right atrium. Recirculation of extracorporeal oxygenated blood compromises extracorporeal gas exchange and increases the possibility of blood trauma. Blood trauma includes undesirable hemolysis, activation of inflammatory processes, or coagulinopathies.
Current double lumen, single cannula for VV ECMO is placed via the jugular vein into the SVC. For the same reason as above, maximum extracorporeal venous drainage is also 50% by discharging the blood primarily from the SVC. The remaining 50% of venous return from the IVC is largely not drained for extracorporeal oxygenation due to the placement of the double lumen single cannula. The existence of only a pediatric system, to the knowledge of the inventors, for this type of VV ECMO is evidence of the fact that the above system is only a partial and unsatisfactory solution. An adult version is simply not available that can drain a sufficient supply of venous blood, oxygenate the blood, and return the blood to the atrium at the flow rates needed for adult ECMO of this type. The blood from IVC can be accessed by further advancement of the cannula into the right atrium to allow some additional blood from the IVC to be drained. However, the extension currently results in significant undesirable recirculation of the blood from and into the atrium, and the resulting undesirable blood trauma described above.
The single lumen cannula tidal flow (VV ECMO) avoids multiple cannulation, but requires a more complicated circuit together with a control system. This type is essentially a batch ECMO, where a quantity of blood is withdrawn from the body through a single lumen, oxygenated external to the body, then returned through the same lumen to the same location in the body. This technology cannot eliminate the recirculation because the drainage and infusion locations are the same. The quantity needs to be small enough to not disturb the hemodynamic flow and yet large enough to provide a substantial amount of oxygenation to the body. High flow blood back and forward in the cannula causes blood trauma, described above.
Recently, three individual venous cannulations (the right jugular vein, and left and right femoral veins) have been reported to achieve near total venous blood drainage without increasing undesirable recirculation (Ichiba, S. et al: Modifying Venous Extracorporeal Membrane Oxygenation Circuit to Reduce Recirculation, Ann Thorac Surg, 2000; 69:298-9). However, the procedure uses three traumatic large venous cannulations and a large extracorporeal volume with long, complicated tubing circuit. Thus, the flow rate and oxygenation is increased, but the trauma to the patient can prevent its wide acceptance for effective VV ECMO.
Therefore, there remains a need for a simple, less invasive, percutaneous cannula system and method.